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Mig Voltage Levels

What advantage does a bigger mig welder have with higher voltage? I understand the longer duty cycle part, just wondering if the voltage makes a difference?

I've always stick welded in the past, so setting a voltage and wire speed is new to me. Setting a current like for stick welding is all I'm familiar with.

Comparing the output graph of volt/amp chart on the millermatic 211 (~ 21V @ 200Amps) versus the millermatic 212 (22V @ 210Amps) versus the millermatic 252 (28V @ 200Amps), what is the advantage of having a higher voltage at the same current?

Is the higher voltage simply needed to run thicker wire at the same current as the next thinner wire? If so is there a recommended voltage range for various current levels on different wire thicknesses?

Simply put, the higher voltage at the same amperage, around 200 amps in this case, translates into more output power or a higher energy arc. Higher energy arc translates into the potential to produce a deeper penetrating weld- less chance of cold lap or lack of fusion to the root.

Also, with the correct gas mix the higher voltage will allow you to use spray arc transfer. 21 or 22 volts isn't going to produce a spray transfer arc, you need a minimum of 24-25 volts, and the correct gas mix for this voltage range. 98 AR/2 Oxy would be the correct mix.

Simply put, the higher voltage at the same amperage, around 200 amps in this case, translates into more output power or a higher energy arc. Higher energy arc translates into the potential to produce a deeper penetrating weld- less chance of cold lap or lack of fusion to the root.

Also, with the correct gas mix the higher voltage will allow you to use spray arc transfer. 21 or 22 volts isn't going to produce a spray transfer arc, you need a minimum of 24-25 volts, and the correct gas mix for this voltage range. 98 AR/2 Oxy would be the correct mix.

The 211 is only 23.5V at 150Amp, so would the 211 then not be adequate for standard mig welding if the spray transfer arc is 24-25V?

To put it in simple terms the more volts means a hotter weld with mig like more amps means a hotter weld for stick. You can run larger dia. wire just like you would use a larger dia. stick electrode.

Many other factors go into it but that is the basic version.

I wonder then why the 211 doesn't indicate the voltage for different welding material thicknesses to compare it to larger welders. Instead they just have there 1..2...3.....10 dial for different thicknesses. I understand the 1-10 is to make it easier for beginners, but what is the difference in setting to a number 1-10 versus a voltage number. Don't think it would be that difficult for a beginner and it would make it easier to tell if the welder wasn't able to handle a certain process if it didn't have high enough voltage.

Bottom line I'm taking off work tomorrow to go buy a new Miller Mig and want to make sure I'm not buying too small of a machine to handle 1/4" to 1/4" T-joint and butt weld joints.

I'm talking welds that I can then take a sledge hammer to and bend the material completely over the weld for testing and the weld NOT break at all.
Can the 211 do those kinds of quality welds?

Page 28 and 29 is the settings chart.
I'm looking at using C25 gas with solid ER70S-6 wire and .035" wire.
So the chart shows 1/4" at dial #6, but it makes it seem 1/4" is easily within the range of the welder. I find it interesting that they do not increase the voltage dial for the thicker wire?

When welding with thicker stick electrodes, a higher current is needed to run the thicker rod properly. Would then a higher voltage setting not be required to run .035 wire versus .030 wire? On the chart they just have both at #6 for 1/4" and the only thing that changes is the feed rate slows down on the thicker wire which is expected since it is depositing more material at once.

You are over complicating this. Look at the manufactures weld output, and thickness range of metals. The comparable number relative to energy output is the rated output amps. If you are wondering what machine to purchase to do 1/4 steel, anything in the miller line from the mm 180 up will handle it with no problem. Obviously you go with larger welders they will have more horsepower and duty cycle. On little mig machines there is no need for actual voltage and wire speed settings, you just get the feel for where you should start your settings and adjust it in from there after some test welds.

Thicker metals conduct heat away from the welding zone so you need more heat and power to get proper penetration. I buy at least one size bigger than I need just incase the metal I weld on is different in quality/metallurgy then the company used for testing. Riding the edge of performance "for me" especially when I'm doing a structural weld adds a bit anxiety and doubt. I've had good looking short circuit Mig welds not even leave a mark on the other 3/16 steel. Why it happened I believe is because I polished the steel to the point it looked like chrome, causing the heat to reflect off of the steel or I hardened the surface of the steel by polishing it. But the incident was eye opening and a good lesson in having enough heat and penetration to do the job.

This might help
The wire feed speed is in direct relation to the amperage at a given wire stickout (length of wire from the contact tip to the arc). The voltage is in the case of a CV (wire welder) the constant and is the length of the arc from the end of the wire to the weld pool, as you change the wire stick out the amperage changes to maintain the weld voltage. A normal wire stick out for short circuit mig welding is 1/4".

The following example may help you understand this with .035 ER70S-6 wire and C25 shield gas set at 20 SCFH flow.
1/4" wire stickout, volts 17 and wire feed speed 150 IPM = 100 amps
3/8" wire stickout, volts 17 and wire feed speed 150 IPM = 50-60 amps due to the resistive heating of the wire between the tip and the arc the weld current drops to the level required to maintain the set voltage.
If you were to reduce the stickout to 1/8" the weld current would increase to approximatly 150 amps to maintain the set voltage.